This depends on your relationship with your artists and the type of gallery you are. Many artists refuse to sell directly and always refer sales through the gallery/galleries that represent them. So their web site would indicate-CONTACT GALLERY/GALLERIES for sales.

Some galleries do not have exclusive or semi-exclusive relationships with their artists [Collectives, etc.] and artists sell through whatever other means are available-directly, on line, etc.

Normally, things sort out over time and you and the artist will figure out where the true value lies-do the majority of their sales come from your gallery or online, or direct, or at art fairs. Once you';re both clear on that, the relationship that makes sense should emerge.